End of use and time duration indicator system and method based on volatile dye

ABSTRACT

A time duration of end of product life indicator is disclosed which utilizes a volatile dye coated or impregnated into a substrate or carrier. The dye evaporates as a volatile component of the product evaporates thereby changing the color of the substrate or carrier. The consumer is alerted to the depletion of the volatile component of the product when the substrate or carrier changes from a colored or dyed state to an uncolored state. As a result, a visual time duration or end of product life indicator is provided.

TECHNICAL FIELD

[0001] The present invention relates generally to an end of product lifeindicator or a time duration indicator for products that include avolatile component. More specifically, the present invention relates tothe use of a volatile dye as an end of product life indicator or a timeduration indicator.

BACKGROUND ART

[0002] Substrates have been commonly used as carriers for air-treatingcompounds, such as insecticides, insect repellents, fragrances anddeodorizing compounds. Insect repellent impregnated substrates andinsecticide-impregnated substrates are useful in both residential andcommercial settings to reduce or eliminate pests. Substrates impregnatedwith fragrances and deodorizing compounds are also useful in bothresidential and commercial settings to reduce or eliminate offensiveodors and to provide a long-lasting pleasant odor. Volatile products mayalso be combined and impregnated into a substrate for combined purposessuch as insect control and deodorization. A variety of differentsubstrates are available and are known to those skilled in the art.

[0003] One disadvantage associated with the use of volatile componentsimpregnated into a substrate is that the consumer is often unaware as towhen the volatile component is depleted or exhausted. As a result, theconsumer is unable to determine when to replace the product. The problemis compounded when the volatile product is a low odor or odor freeinsecticide. However, even when the volatile product is a fragrance or adeodorizing composition, consumers are often unable to determine whenthe product should be replaced for optimum product performance.Specifically, when relying upon the sense of smell, it is difficult todetermine when a fragrance or a deodorizing component has beensubstantially depleted to a point where the product is no longereffective.

[0004] U.S. Pat. No. 4,921,636 teaches a visual indicator whereby thecarrier or substrate is transparent or translucent when impregnated witha volatile product containing a solvent. As the solvent evaporates, thesubstrate or carrier becomes more opaque thereby providing a visual endof product life indicator for the consumer. However, this visual end ofproduct life indicator is problematic because of the insufficientcontrast between a light or white carrier and a partially transparenttranslucent carrier. A preferable indicator would include a sharp colorchange.

[0005] A color change indicator is disclosed in U.S. Pat. No. 4,824,827,assigned to the assignee of the present application. The color changetaught in the '827 patent depends upon a pH change. The dye utilized issubstantially non-volatile.

SUMMARY OF THE INVENTION

[0006] According to one aspect of the present invention, a time durationindicating system for a product that includes a volatile componentcomprises a substrate and a volatile dye. The substrate is coated withthe volatile dye thereby coloring the substrate. As the volatile dyeevaporates over time, the substrate changes color.

[0007] According to a further aspect of the present invention, a methodfor indicating an end of life for a product that includes a substrateimpregnated with a volatile component comprises the step of coating asubstrate with a volatile dye thereby coloring the substrate. As thevolatile dye volatilizes over time, a color change of the substrateresults.

[0008] According to yet another aspect of the present invention, aninsecticide product with an end of life color change indicator includesa substrate and a volatile insecticide coated onto the substrate. Thevolatile insecticide is selected from the group consisting oftransfluthrin, vapothrin, permethrin, prallethrin, tefluthrin andesbiothrin and guaiazulene is coated onto the substrate.

[0009] Other aspects and advantages of the present invention will becomeapparent upon consideration of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 illustrates, graphically, the data presented in Table 1and, more specifically, a color change provided by an indicator systemmade in accordance with the disclosure after approximately 5.8 hours;

[0011]FIG. 2 illustrates, graphically, the performance of the indicatortested in Table 1 and FIG. 1 on subsequent days thereby illustrating thereproducibility of the data presented in Table 1 and FIG. 1;

[0012]FIG. 3 illustrates, graphically, the data of Table 3 and, moreparticularly, the effect of dye concentration on indicator duration;

[0013]FIG. 4 illustrates, graphically, the data of Table 5 and, moreparticularly, the effect of prallethrin concentration as a retarder onindicator duration;

[0014]FIG. 5 illustrates, graphically, the data of Table 6 and, moreparticularly, the effect of esbiothrin concentration as a retarder onindicator duration;

[0015]FIG. 6 illustrates, graphically, the data of Table 7 and, moreparticularly, the effect of transfluthrin concentration as a retarder onindicator duration;

[0016]FIG. 7 illustrates, graphically, the data presented in Table 9and, more specifically, the effect of air velocity on indicatorduration;

[0017]FIG. 8 illustrates, graphically, the data presented in Table 10and, more specifically, the effect of air temperature on indicatorduration without the presence of a retarder, such as an insecticide;

[0018]FIG. 9 illustrates, graphically, the data of Table 11 and, morespecifically, the effect of temperature on indicator duration withtransfluthrin included as a retarder;

[0019]FIG. 10 illustrates, graphically, the data of Table 12 and, morespecifically, the effect of temperature on indicator duration withprallethrin included as a retarder;

[0020]FIG. 11 illustrates, graphically, the data of Table 13 and, morespecifically, the effect of temperature on indicator duration withesbiothrin included as a retarder;

[0021]FIG. 12 illustrates, graphically, the data presented in Table 16and, more specifically, the rate of evaporation of transfluthrin from aninert plastic substrate;

[0022]FIG. 13 is a plane view of a color change indicator and referencetemplate; and

[0023]FIG. 14 is a plane view of another color change indicator andreference template.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention discloses the use of a volatile dye as acolor change indicator for a product that includes a volatile component,such as a fragrance, odor treating chemical, insect repellent orinsecticide. One preferred volatile dye is guaiazulene(1,4-dimethyl-7-(1-methylethylazulene). Other volatile dyes can be usedwith products and methods of the present invention. Guaiazulene is ablue oil that is know for its anti-inflammatory and anti-ulcerativeproperties. Once source of guaiazulene is Arcos Organics N.V. (CAS)#489-84-9). Guaiazulene has a boiling point of 153° C. at 7.00 mm Hg.Guaiazulene is stable under normal temperatures and pressures. Uponinitial application, guaiazulene imparts a blue color to a substrate andthe blue color substantially fades or visually disappears as shownbelow.

[0025] It is preferable to dissolve the dye in an organic solvent. Useof the solvent as a carrier medium facilitates the application of thedye in a uniform manner to the substrate or carrier. The solvent can bepolar or nonpolar and should be sufficiently volatile to evaporateduring the process of drying after the application of the dye. Possiblesolvents include, but are not limited to, ISOPAR™ C, ISOPAR™ E, ISOPAR™L, heptane, methanol, acetone, ethanol, isopropyl alcohol, dodecene andtetraydrofuran. ISOPAR™ C, ISOPAR™ E and ISOPAR™ L are hydrocarbonsolvents of varying chain length and are available from Exxon ChemicalCompany.

[0026] The substrate or carrier can be fabricated from any material thatis capable of absorbing the intermediate solution containing the dye.The absorption may take place take place either on the substrate orcarrier surface or the substrate may be capable of being impregnatedwith the intermediate solution. The dye must be able to impart a colorthat is substantially different from the untreated substrate or carrier.The substrate must also allow for a free availability of the dye forslow evaporation when brought in contact with the ambient atmosphere.Examples of suitable substrate or carrier materials include, but are notlimited to, cellulose, glass fiber filters, synthetic paper materials,ceramic materials, textiles, felt-type materials, wovens and nonwovens,bonded or sintered synthetic or natural polymer powders and the like.

[0027] Use of the terms “coated” or “coating” in connection with theapplication of the volatile dye is intended to cover adsorption,absorption, adhesion, impregnation, application or any other phenomenonthat allows the volatile dye to be subsequently borne by the substrateor vaporize from the substrate.

[0028] In the data presented in the following Tables and Figuresattached hereto, the substrate used was Whatman type 2 filter paper(catalogue no. 1002 240) which has a 8 μm pore size and is 7.5 milthick. The filter paper was used in 1 inch circular discs. The paper wasaffixed to an inert heavy plastic base using conventional glue orcement. A computer controlled wind tunnel that is capable of achievingtemperatures up to 40° C. and up to 8 m/s air velocities was used totest the effects of wind, speed and temperature on the indicator. It wasfound that guaiazulene, in a concentration of 50-500 μg/cm² on filterpaper provided a suitable color change indicator.

[0029] A colorimeter was used to measure color change numerically. TheL*a*b* color space (also referred to as CIELAB) was utilized. In thiscolor space, L* indicates lightness and a* and b* are the chromaticitycoordinates. The a* and b* indicate color directions: +a* is the reddirection, −a* is the green direction, +b* is the yellow direction, and−b* is the blue direction. The center is achromatic; as the a* and b*values increase and moves out from the center, the saturation of thecolor increases.

[0030] Colorimeters are also widely used to detect color differencesvery accurately. In the L*a*b* color space, color difference can beexpressed as a single numeric value, _(.)ΔE*_(ab), which indicates thesize of the color difference but not in what way the colors aredifferent. _(.)ΔE*_(ab) is defined by the following equation:_(.)ΔE*_(ab)=[(ΔL*)²+(Δa*)²+(Δb*)²]^(0.5).

[0031] In the following experiments, the color of a substrateimpregnated with the same dye in time space as it is fading wasrecorded. During the process of fading, the L* (lightness) increases invalue, the −b* value (blue color) decreases in value and approaches theorigin (achromatic center) and the a* value remains predominantlyunchanged. As a result, the _(.)ΔE*_(ab) increases as the sample fadesand hence accurately represents the color differences perceived by thehuman eye. The _(.)ΔE*_(ab) value measured is with respect to a blanksubstrate since that is the color the substrate would eventually reachif all the dye evaporates and does not leave a residual color. It wasobserved that when _(.)ΔE*_(ab) is 10 or less, the color of thesubstrate more or less resembles the blank substrate to a human eye andhence, a _(.)ΔE*_(ab) value of 10 was selected as a depleted value. The_(.)ΔE*_(ab) could go down for some indicators before it stabilizes at aconstant value but a decrease below 10 is not noticeable to the humaneye.

[0032] A Minolta CR-310 Chroma Meter is used for quantifying the colorand measuring the color differences. It is a compact tristimulus coloranalyzer for measuring reflective colors of surfaces. This colorimeterhas an 8 mm-diameter measuring area and uses diffuse illumination and azero degrees viewing angle (specular component included). Absolutemeasurements are made in L*a*b* (CIE 1976) values.

[0033] In the following examples, at least three samples were consideredfor color measurements and the average values are reported.

EXAMPLE 1 Colorimeter Measurements on Indicators

[0034] Indicators were prepared by micropipetting 75 μL of 1 wt % dyesolution in Ispoar E on 1 inch diameter circular Whatman type 2 (VWRCatalogue no. 1002 240) filter paper substrate. This corresponds to adye surface density of 107 μg/cm². The samples were exposed in a windtunnel at 1 m/s air velocity at a temperature of 26.6° C. While thesample was fading, calorimeter measurements were carried out and colordifference from the untreated sample was calculated and shown in Tableand FIG. 1. Results indicate that the initial color of the indicator isblue and slowly fades off with time until the final color reaches aplateau value that almost corresponds to that of untreated sample. Theduration of the indicator as determined by a color difference value of10 units from an undyed substrate is about 5.8 hours. This indicatorsystem can be practically used to indicate the end-point of 5.8 hours inan environment with an air flow of 1 m/s and a temperature of 26.6° C.TABLE 1 Colorimeter Measurements on Guaiazulene Dye Indicator System AirVelocity 1 m/s Temperature 26.6° C. (80° F.) Substrate 1 in circulardia. Filter paper substrate Intermediate Volume 75 μL Solvent ISOPAR ™ EDye Level 107 μg/cm² Average of Sample Hours Color Space 6 readings Std.Dev _(.)ΔE*_(ab) Untreated — L* 95.14 0.09 0.00 Substrate a* 0.02 0.02b* 0.54 0.01 Treated 0 L* 70.96 0.71 30.77 Substrate a* 0.58 0.14 b*−18.47 0.47 1 L* 75.10 0.49 24.48 a* −0.70 0.28 b* −13.50 1.10 2 L*77.52 0.93 20.80 a* −1.43 0.34 b* −10.41 1.69 3 L* 79.96 1.44 17.16 a*−2.00 0.35 b* −7.19 2.46 4 L* 82.19 1.86 13.89 a* −2.48 0.25 b* −3.803.10 5 L* 84.27 1.45 11.29 a* −2.71 0.11 b* −0.84 2.58 6 L* 85.87 1.209.73 a* −2.77 0.08 b* 1.50 2.08 7 L* 87.16 0.89 8.94 a* −2.73 0.14 b*3.49 1.40 8 L* 87.73 0.84 8.89 a* −2.71 0.12 b* 4.63 0.78 9 L* 88.090.81 8.73 a* −2.52 0.16 b* 5.02 0.81 10 L* 88.52 0.77 8.72 a* −2.59 0.16b* 5.57 0.68 11 L* 88.70 0.78 8.72 a* −2.51 0.18 b* 5.85 0.57 12 L*88.94 0.77 8.63 a* −2.42 0.19 b* 6.02 0.49 13 L* 89.20 0.86 8.48 a*−2.35 0.19 b* 6.11 0.44 14 L* 89.41 0.86 8.29 a* −2.30 0.18 b* 6.06 0.4315 L* 89.52 0.79 8.12 a* −2.24 0.18 b* 5.95 0.42

EXAMPLE 2 Reproducibility of Indicator Duration in Lab Tests

[0035] Indicators used in Example 1 were subjected to testing underidentical environmental conditions (temperature and air velocity) onfour different days to check the reproducibility of the indicatorduration in test conditions _(.)ΔE*_(ab) values as a function of timefor each of the four trials are shown in FIG. 2 and in Table 2. Resultsindicate that the experiments conducted in the wind tunnel are highlyreproducible. TABLE 2 Reproducibility of Indicator Duration Air Velocity1 m/s Temperature 26.6° C. (80° F.) Substrate 1 in circular dia. Filterpaper substrate Intermediate Volume 75 μL Solvent ISOPAR ™ E Dye Level107 μg/cm² Hours Trial #1 Trial #2 Trial #3 Trial #4 0 30.8 30.85 30.1532.32 1 24.5 25.55 — 25.46 2 20.8 22.46 19.46 22.33 3 17.2 — — 19.41 413.9 14.75 14.14 15.96 5 11.3 — — 12.76 6 9.7 10.11 8.72 8.84 7 8.9 — —8.00 8 8.9 7.84 7.79 7.73 9 8.7 — — 7.85 10 8.7 8.14 8.20 7.94 11 8.7 —— 8.15 12 8.6 8.04 7.64 — 13 8.5 — — — 14 8.3 7.76 7.05 —

EXAMPLE 3 Effect of Dye Concentration on Indicator Duration

[0036] Four different dye levels with surface densities ranging from26.6 μg/cm² to 107 μg/cm² were tested in the wind tunnel at 32.2° C. at1 m/s air velocity and indicator durations were determined. Results, asshown in Table 3 and FIG. 3, indicate that the indicator durationuniquely depends on the dye level and it increases with dye level. Thus,indicators with specific duration can be prepared by applying anappropriate level of dye. TABLE 3 Effect of Dye Level on IndicatorDuration Substrate 1 in diameter Filter paper Intermediate Volume 75 μLSolvent ISOPAR ™ E Temperature 32.2° C. (90° F.) Air Velocity 1 m/s DyeLevel Indicator Duration (hours) 26.6 μg/cm² 0.8 53.3 μg/cm² 3.1 79.9μg/cm² 5.4  107 μg/cm² 18.7

EXAMPLE 4 Effect of Retarder on Indicator Duration

[0037] A retarder can be added to the intermediate solution to “tune”the indicator duration. Any relatively low volatile organic chemicalthat is chemically compatible can be used as a retarder. A retarderusually retards the evaporation of the dye and thus prolongs theindicator duration. The extent of prolonging the end point depends onthe type of the retarder utilized. Some retarders prolong the endpointto as many at 18 hours while others do not significantly affect theindicator duration. Table 4 illustrates the effect of some of theretarders on the indicator duration. As shown in Tables 5, 6 and 7 andFIGS. 4-6, respectively, increasing the retarder surface density on thesubstrate at the same dye level increases the indicator duration. Addingtwo parts of retarder for each part of dye extended the indicatorduration by as much as a factor of three as shown in Tables 5, 6 and 7.Surprisingly, the indicator duration is directly proportional to theamount of retarder used in the system (compare with Table 3 whichillustrates the rapid increase in indicator duration with dye level).TABLE 4 Effect of Retarder Type on Indicator Duration Substrate 1 indiameter Filter paper Intermediate Volume 75 μL Solvent ISOPAR ™ E DyeLevel 107 μg/cm² Retarder Level 213 μg/cm Temperature 26.6° C. (80° F.)Air Velocity 1 meter/second Retarder Type Indicator Duration (hours)None 5.8 Hexadecane 5.5 Tetradecene 5.6 Dodecene 8.3 Deet 9.9 Vapothrin14.0 Permethrin 14.0 Prallethrin 15.9 Tefluthrin 17.0 Esbiothrin 17.7

[0038] TABLE 5 Effect of Prallethrin Level on Indicator DurationSubstrate 1 in diameter Filter paper Intermediate Volume 75 μL SolventISOPAR ™ E Dye Level 107 μg/cm² Temperature 26.6° C. (80° F.) AirVelocity 1 meter/second Prallethrin Surface Density Indicator Duration(hours)  0.0 μg/cm²   5.7 53.3 μg/cm   6.6 107 μg/cm² 11.6 213 μg/cm²15.9

[0039] TABLE 6 Effect of Esbiothrin Level on Indicator DurationSubstrate 1 in diameter Filter paper Intermediate Volume 75 μL SolventISOPAR ™ E Dye Level 107 μg/cm² Temperature 26.6° C. (80° F.) AirVelocity 1 meter/second Esbiothrin Surface Density Indicator Duration(hours)  0.0 μg/cm²   5.7 53.3 μg/cm²  8.7 107 μg/cm² 13.2 213 μg/cm²17.7

[0040] TABLE 7 Effect of Transfluthrin Level on Indicator DurationSubstrate 1 in diameter Filter paper Intermediate Volume 75 μL SolventISOPAR ™ E Dye Level 107 μg/cm² Temperature 26.6° C. (80° F.) AirVelocity 1 meter/second Transfluthrin Surface Density Indicator Duration(hours) 0.0 μg/cm² 5.7 53.3 μg/cm²  8.5  107 μg/cm²   14.5

[0041] The results of Table 7 are shown graphically in FIG. 6.

EXAMPLE 5 Effect of Solvent on Indicator Duration

[0042] The solvent, being high volatile relative to the dye, is expectedto evaporate rapidly during the drying process leaving the dye behind toevaporate more slowly at a later period. However, contrary to ourexpectations, Table 8 illustrates that the type of solvent used to applythe dye on the substrate can have a strong influence on the indicatorduration. Solvents with high Hansen polar solubility component appear tolead to significantly prolonged indicator duration as opposed to thosethat are relatively non-polar in nature. This dependence is againattributed to chemical interactions that are present between the dye andthe solvent. TABLE 8 Effect of Solvent on Indicator Duration Substrate 1in diameter Filter paper Intermediate Volume 75 μL Solvent ISOPAR ™ EDye Level 107 μg/cm² Temperature 26.6° C. (80° F.) Air Velocity 1meter/second Solvent Indicator Duration (hours) Isobutyl Acetate 5.3hours Acetone 8.0 hours Methanol 10.9 hours  IPA 13.3 hours  Ethanol12.5 hours  ISOPAR ™ E 5.7 hours

EXAMPLE 6 Effect of Air Velocity on Indicator Duration

[0043] Increasing air velocity decreases the indicator duration as showin Table 9 and FIG. 7 for indicator systems with and without retarders.This is expected since increasing air velocity accelerates theevaporation rate of the dye as well as the retarder. TABLE 9 Effect ofAir Velocity on Indicator Duration Substrate 1 in diameter Filter paperIntermediate Volume 75 μL Solvent ISOPAR ™ E Temperature 26.6° C. (80°F.) Indicator Duration (hours) Indicator System V = 1 m/s V = 3 m/s V =6 m/s 53.3 μg/cm^(2 Dye) Dye 1.7 1.0 0.9 107 μg/cm² Dye 5.8 3.9 1.8 107μg/cm² Dye + 53.3 μg/cm² 8.5 4.9 2.7 Transfluthrin 107 μg/cm² Dye + 107μg/cm² 14.5 5.9 3.8 Transfluthrin 107 μg/cm² Dye + 533 μg/cm² 43.9 31.512.6 Transfluthrin

EXAMPLE 7 Effect of Temperature on Indicator Duration

[0044] Tables 10-13 and FIGS. 8-11, respectively, show the effect oftemperature on indicator duration for indicator systems without retarder(Table 10; FIG. 8), with Transfluthrin as a retarder (Table 11; FIG. 9),with Prallethrin as a retarder (Table 12; FIG. 10), with Esbiothrin as aretarder (Table 13; FIG. 11). Clearly, there is a general trend ofindicating decreasing indicator durations with increasing ambienttemperatures. TABLE 10 Effect of Temperature on Indicator DurationWithout Retarder Substrate 1 in diameter Filter paper IntermediateVolume 75 μL Solvent ISOPAR ™ E Air Velocity 1 m/s Indicator DurationDye Surface Density T = 26.6° C. T = 32.2° C. T = 37.7° C. 26.6 μg/cm²0.7 0.67 0.4 53.3 μg/cm² 1.7 1.08 0.9 79.9 μg/cm² 3.1 2.1 1.8  107μg/cm² 5.8 4.38 3.5

[0045] TABLE 11 Effect of Temperature on Indicator Duration WithTransfluthrin as Retarder Substrate 1 in diameter Filter paperIntermediate Volume 75 μL Solvent ISOPAR ™ E Dye Level 107 μg/cm² AirVelocity 1 m/s Indicator Duration (hours) Transfluthrin Level T = 26.6°C. T = 32.2° C. T = 37.7° C. 53.3 μg/cm²  8.5 6.2 2.9 107 μg/cm² 14.58.4 3.8 553 μg/cm² 43.9 47.0 13.3

[0046] TABLE 12 Effect of Temperature on Indicator Duration WithPrallethrin as Retarder Substrate 1 in diameter Filter paperIntermediate Volume 75 μL Solvent ISOPAR ™ E Dye Level 107 μg/cm² AirVelocity 1 m/s Indicator Duration (hours) Prallethrin Surface Density T= 26.6° C. T = 32.2° C. T = 37.7° C. 53.3 μg/cm²  6.6 5.5 3.8 107 μg/cm²11.6 9.9 7.4 213 μg/cm² 15.9 15.5 13.8

[0047] TABLE 13 Effect of Temperature on Indicator Duration WithEsbiothrin as Retarder Substrate 1 in diameter Filter paper IntermediateVolume 75 μL Solvent ISOPAR ™ E Dye Level 107 μg/cm² Air Velocity 1 m/sIndicator Duration (hours) Esbiothrin Surface Density T = 26.6° C. T =32.2° C. T = 37.7° C. 53.3 μg/cm²  8.7 6.7 4.1 107 μg/cm² 13.2 13.4 8.8213 μg/cm² 17.7 23.5 11.2

[0048] Tables 14 and 15 illustrate the effect of temperature on systemswith different solvents (Table 14) and different retarders (Table 15).TABLE 14 Effect of Temperature on Indicator Duration With DifferentSolvents Substrate 1 in diameter Filter paper Intermediate Volume 75 μLDye Level 107 μg/cm² Indicator Duration (hours) T = 22.2° C. T = 26.6°C. T = 32.2° C. Solvent V = 0 m/s V= 1 m/s V = 1 m/s Isobutyl Acetate18.7 5.3 4.0 Acetone 29.3 8.0 6.0 Methanol n/a* 10.9 11.0  IPA n/a* 13.3  n/a*  Ethanol n/a* 12.5 14.3  ISOPAR ™ E n/a* 5.7 4.6

[0049] TABLE 15 Effect of Temperature on Indicator Duration forDifferent Retarders Substrate 1 in diameter Filter paper IntermediateVolume 75 μL Solvent ISOPAR ™ E Dye Level 107 μg/cm² Retarder Level 213μg/cm² Indicator Duration (hours) T = 22.2° C. T = 26.6° C. T = 32.2° C.Retarder Type V = 0 m/s V = 1 m/s V = 1 m/s None n/a* 5.8 4.6 Hexadecane16.2 5.5 4.9 Tetradecene 10.4 5.6 3.4 Transfluthrin 27.9 7.2 21.8Dodecene 11.3 8.3 3.5 Deet 56.8 9.9 7.0 Vapothrin 46.0 14.0 8.0Permethrin n/a* 14.0 15.4 Prallethrin n/a* 15.9 21.1 Tefluthrin n/a*17.0 18.3 Esbiothrin n/a* 17.7 23.5

EXAMPLE 8 Sensitivity to Ambient Conditions

[0050] Table 3 and FIG. 3 illustrate that the indicator duration is notlinearly related to the level of dye while Tables 5-7 and FIGS. 4-6,respectively, suggest the linearity of indicator duration with the levelof retarder present in the indicator system.

[0051] There are many systems whose performance depends on evaporationof a chemical from an impregnated substrate such as insecticidal stripor a fragrance strip. The parameters that affect the evaporation of suchan active are primarily temperature of the surroundings, and velocity ofair blowing over the system. It has been proven in chemical engineeringliterature that, for such a system, evaporation rate of the active isdirectly proportional to the square root of the velocity of the airblowing over the system. In addition, pure components typically followthe Clausius-Clapeyron equation, which states that the natural logarithmof vapor pressure is directly proportional to the inverse of absolutetemperature. Since evaporation rate is directly proportional to thevapor pressure, it can be deduced that the evaporation rate is alsorelated to temperature in a similar fashion for pure components.Intuitively, it appears that product life is inversely related toevaporation rate. The higher the evaporation rate, the lower will be theproduct life. In fact, it can be proven mathematically that product lifeis inversely proportional to the evaporation rate. Also, again, onintuitive grounds, it said that product life is directly proportional tothe total amount of active available for evaporation. Based on thesereasoning, it is concluded that, for pure component systems:

[0052] (a) product life is directly proportional to the amount of activepresent in the system;

[0053] (b) product life is inversely proportional to the square root ofthe velocity of air blowing over the system; and

[0054] (c) natural logarithm of the inverse of product life is directlyproportional to the inverse of absolute temperature.

[0055] Keeping the above correlations in mind, we will now see how theindicator duration is influenced by the retarder level or dye levelpresent in the indicator system, ambient air velocity, and temperature.

[0056] Table 3 illustrates that the indicator duration is not linearlyrelated to the level of dye while tables 5, 6, and 7 suggest thelinearity of indicator duration with the level of retarder present inthe indicator system. Thus, the indicator system responds in the samemanner that the passive evaporation product responds to the dose level.Both indicator duration and product life are directly proportional toactive level.

[0057] Table 9 and FIG. 7 illustrate that the indicator duration isinversely proportional to the square root of the air velocity asillustrated by a negative slope suggesting that the indicator durationalso responds in the same manner the product does to the air velocity.When air velocity increases, product duration decreases and indicatorduration also decrease by the same extent.

[0058] In Tables 10 and 11, and FIGS. 8-9, respectively, the naturallogarithm of inverse of indicator duration (which correlates withnatural logarithm of evaporation rate of the dye) is plotted as afunction of inverse of absolute temperature. For system containing puredye, the regressed lines are linear and parallel to each other. Thelinear nature of the lines suggests that the dye system follows theClausius-Clapeyron equation, which is derived from thermodynamicfundamentals. The parallel nature of the lines confirm the accuracy ofthe experiments once again since the slope depends only on the type ofchemical used on the substrate but not on the amount of chemical used.Since the same dye is used at different levels in Table 10 and FIG. 8,the lines are expected to be parallel to each other. In the former case,the slope corresponds uniquely to the dye where as in the latter case,the slope corresponds primarily to the retarder since the retarder isthe determining factor for the indicator duration. A similar plot isshown in Table 11 and FIG. 9 for a constant level of dye and differentlevels of Transfluthrin. All lines are linear and are parallel to eachother suggesting that the dye and retarder system behaves like a singlecomponent system. The mixture, at different compositions of dye andretarder, behaving as a single component is unexpected.

[0059] In an unrelated experiment, 5 mg of Transfluthrin coated on aplastic substrate having dimensions of 2″×8″ was placed in a wind tunneland maintained at an air velocity of 5 m/s and an air temperature of 80°F. The Transfluthrin was thereafter allowed to evaporate for six hours.The strip was then removed from the wind tunnel and evaluated todetermine the residual unevaporated amount remaining on the strip. Basedon this, average evaporation loss per hour was determined. Product lifewas then estimated based on the knowledge that 5 mg of active was placedon the strip at the start. The experiment was repeated at 90° F. and100° F. air temperatures. The logarithm of the inverse of product lifewas plotted as a function of the inverse of absolute temperature. Theregressed line was a straight line with a negative slope suggesting thatthe evaporation of Transfluthrin from a plastic strip follows theClausius-Clapeyron equation, which was to be expected inasmuch as thesamples comprised a uniformly evaporating single component. While theslope of the regressed line was −10.2 units (see Table 16 and FIG. 12),the slope of a similarly regressed line from a dye with Transfluthrin asa retarder system (see Table 11 and FIG. 9) was −10.0 units. Theseslopes can be considered identical within the range of experimentalerror. However, for the indicator system without a retarder, the averageslope was −4.7 units, which is quite different than the above twoslopes. As shown in Tables 12 and 13 and FIGS. 10 and 11, respectively,the average slopes for Prallethrin and Esbiothrin are −3.2 units and−4.4 units, which are, again, quite different from that ofTransfluthrin. This suggests that the indicator with Transfluthrin as aretarder responds to temperature in the same manner that a passiveevaporating system with Transfluthrin would. The dye and Transfluthrinmixture behaves more like pure Transfluthrin in terms of the vaporpressure dependency thereof on temperature (instead of displaying anintermediate behavior).

[0060] In summary, for a passively evaporating product that contains aslowly evaporating chemical, an indicator system can be chosen utilizingthe same evaporating chemical as a retarder to indicate the end point ofthe product. Surprisingly, both the product and the indicator system insuch a composition responds in exactly the same fashion to variations inthe ambient temperature and air velocity, and hence, the indicatorsystem continues to indicate the end point of the product irrespectiveof variations in ambient conditions. This is because the rate at whichthe indicator system loses the retarder strongly correlates to the rateat which the active evaporates from the product at any temperature andair flow that the product might be subjected to. TABLE 16 TransfluthrinEvaporation From an Inert Plastic Substrate Temperature (° F.) Velocity(m/s) 6 hr Release (mg) Product Life 80 5 1.13 26.5 90 5 2.5 12.0 100 53.83 7.8

EXAMPLE 9 Stability of Indicator Samples

[0061] Dye samples with and without retarder that were used in all theabove examples were prepared and color measurements were noted. Thesamples were then sandwiched between two transparent glass sheets. Theedges of the glass plates were glued together hermetically using rubbercement. A total of three sets of experimental samples were prepared ofwhich, one set was exposed on the bench top at 72° F., the second setwas kept in the over at 130° F., and the third set was stored in arefrigerator at 32° F. The difference in color between the period, asmeasured by the quantity _(.)ΔE*_(ab) was measured and shown in Table17. As shown, the samples stored at or below room temperature aresufficiently stable compared to those stored at higher temperature.TABLE 17 Stability Results Substrate 1 in diameter Filter paperIntermediate Volume 75 μL Solvent ISOPAR ™ E Dye Level 107 μg/cm²Retarder Level 213 μg/cm² _(.)E_(ab) 32 deg. F. 72 deg. F. 130 deg. F.Retarder Type 0 days 1 month 1 day 1 0 days 1 No Retarder 29.6 28.5 26.822.5 28.7 19.4 2% Transfluthrin 34.5 31.3 35.7 26.9 33.7 23.2 2% Etoc35.1 32.6 34.9 25.9 35.2 22.5 2% EBT 29.7 26.8 31.9 25.6 32.9 22.9 2%Vapothrin 29.6 32.3 31.5 28.4 32.2 16.2

[0062]FIG. 13 illustrates an embodiment where a color change indicator10 made in accordance with the principles discussed above is surroundedby a reference template 12 divided into five sections 13-17. The section17 is indicative of the darkness of the indicator 10 when the indicator10 is freshly coated with the volatile dye. Section 16 is indicative ofthe color of the indicator 10 when a portion of the dye has evaporated,such as approximately 25%. Thus, section 16 provides a color referencefor an indicator that has approximately 75% of its dye (and thereforeproduct) unvolatilized. Sections 15, 14 and 13 are all progressivelylighter in hue and are indicative of the color of the indicator 10 whenit has approximately 50%, approximately 25% and approximately 0% of thedye and product remaining respectively. A similar indicator 20 andreference template 21 is shown in FIG. 14. The reference template 21 isdivided into five sections 22-26 which roughly correspond to the amountof dye and product remaining as the sections 13-17 discussed above. Thatis, the lack of color in section 22 is indicative of a substantiallydepleted product. The darkness of section 23 is indicative of anindicator 20 with approximately 25% of the dye and product remainingwhile the sections 24, 25 and 26 represent the darkness of the indicator20 with approximately 50%, approximately 75% and approximately 100% ofthe dye and product remaining respectively.

INDUSTRIAL APPLICABILITY

[0063] The present invention comprehends a use-up cue for practicalapplication to any of a number of volatile dispensing products. A methodof manufacturing and/or using such a use-up cue is also disclosed.

[0064] The foregoing description is given for clearness of understandingonly, and no unnecessary limitation should be understood therefrom, asmodifications within the scope of the invention may be apparent to thoseskilled in the art.

We claim:
 1. A time duration indicating system for a product thatincludes a volatile component, the system comprising: a substrate, and avolatile dye, the volatile dye being coated onto the substrate therebycoloring the substrate, the volatile dye evaporating over time resultingin a color change for the substrate.
 2. The time duration indicatingsystem of claim 1, wherein the volatile component is an insecticide. 3.The time duration indicating system of claim 2, wherein the insecticideis a pyrethroid.
 4. The time duration indicating system of claim 2,wherein the insecticide is selected from the group consisting oftransfluthrin, vapothrin, permethrin, prallethrin, tefluthrin andesbiothrin.
 5. The time duration indicating system of claim 1, whereinthe volatile component is N,N-diethyl-m-toluamide.
 6. The time durationindicating system of claim 1, wherein the volatile dye is guaiazulene.7. The time duration indicating system of claim 1, wherein the volatiledye is guaiazulene and the volatile component is transfluthrin.
 8. Thetime duration indicating system of claim 1, further comprising asolvent, the volatile dye being dissolved in the solvent to form anintermediate solution, the substrate being coated with the intermediatesolution.
 9. The time duration indicating system of claim 8, wherein thesolvent is selected from the group consisting of ISOPAR™ C, ISOPAR™ E,ISOPAR™ L, heptane, methanol, acetone, ethanol, isopropyl alcohol,dodecene and tetrahydrofuran or mixtures thereof.
 10. The time durationindicating system of claim 1, wherein the substrate is made from amaterial selected from the group consisting of cellulose, matted glassfibers, paper, ceramic, felt, woven fabric, nonwoven fabric, andpolymeric powders or mixtures thereof.
 11. The time duration indicatingsystem of claim 1, further comprising a retarder selected from the groupconsisting of hexadecane, tetradecene, transfluthrin, dodecene,N,N-diethyl-m-toluamide, vapothrin, permethrin, prallethrin, tefluthrin,and esbiothrin.
 12. The time duration indicating system of claim 1,further comprising a reference template having a color substantially thesame as the substrate coated with the volatile dye and prior to anysubstantial volatilization of said dye.
 13. The time duration indicatingsystem of claim 1, further comprising a reference template having acolor substantially the same as the substrate after substantially all ofthe dye has been volatized.
 14. The time duration indicating system ofclaim 1, wherein the volatile component is an insect repellant.
 15. Amethod for indicating an end of life of a product that includes asubstrate coated with a volatile component, the method comprising:coating the substrate with a volatile dye thereby coloring thesubstrate, the volatile dye volatilizing over time resulting in a colorchange for the substrate.
 16. The method of claim 15, wherein thevolatile dye is guaiazulene and the volatile component is aninsecticide.
 17. The method of claim 15, wherein the volatile dye isguaiazulene and the volatile component is transfluthrin.
 18. The methodof claim 15, further comprising the steps of providing a solvent, andmixing the volatile dye with the solvent to form an intermediatesolution, wherein the coating step further comprises coating thesubstrate with the intermediate solution.
 19. The method of claim 18,wherein the intermediate solution further comprises a retarder.
 20. Themethod of claim 18, wherein the retarder is selected from the groupconsisting of hexadecane, tetradecene, transfluthrin, dodecene,N,N-diethyl-m-toluamide, vapothrin, permethrin, prallethrin, tefluthrin,and esbiothrin.
 21. The method of claim 15, further comprising the stepsof providing a retarder, and mixing the volatile dye with the retarder,wherein the coating step further comprises coating the substrate withthe volatile dye and the retarder.
 22. The method of claim 20, whereinthe retarder is selected from the group consisting of hexadecane,tetradecene, transfluthrin, dodecene, N,N-diethyl-m-toluamide,vapothrin, permethrin, prallethrin, tefluthrin, and esbiothrin.
 23. Aninsecticide product with an end of life color change indicator,comprising: a substrate, a volatile insecticide coated onto thesubstrate, the volatile insecticide selected from the group consistingof transfluthrin, vapothrin, permethrin, prallethrin, tefluthrin andesbiothrin, and guaiazulene coated onto the substrate.
 24. Theinsecticide product of claim 23, further comprising a reference templatedisposed adjacent to the substrate and having a color substantially thesame as the substrate coated with the guaiazulene dye and prior tovolatilization of the guaiazulene dye.
 25. The insecticide product ofclaim 23, further comprising a reference template disposed adjacent tothe substrate and having a color substantially the same as the substrateafter substantially all of the guaiazulene dye has been volatized.